[PATCH] Cygwin: console: Release pipe_sw_mutex in pcon_hand_over_proc()

[Corinna Vinschen]

On Mar 25 22:06, Takashi Yano wrote:
> Currently, pipe_sw_mutex is held in the process which is running
> in console inherited from pseudo console until the process ends.
> Due to this behaviour, the process may cause deadlock when it
> attempts to acuqire input_mutex in set_input_mode() called via
              acquire

> close_ctty(). This deadlock occurs because the pty master
> acuires input_mutex first and acuire pipe_sw_mutex next while
  acquire                       acquire

> the process exiting acuire pipe_sw_mutex first.
                      acquire

> To avoid this deadlock, this patch releases pipe_sw_mutex in
> pcon_hand_over_proc(). In addition, pointless pipe_sw_mutex
> acquire/release is drppped in pcon_hand_over_proc().
> 
> Fixes: 04f386e9af99 ("Cygwin: console: Inherit pcon hand over from parent pty")
> Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
> Reviewed-by:
> ---
>  winsup/cygwin/fhandler/console.cc | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/winsup/cygwin/fhandler/console.cc b/winsup/cygwin/fhandler/console.cc
> index 29cdba0d3..1dd5dfa1d 100644
> --- a/winsup/cygwin/fhandler/console.cc
> +++ b/winsup/cygwin/fhandler/console.cc
> @@ -1994,8 +1994,6 @@ fhandler_console::pcon_hand_over_proc (void)
>    char buf[MAX_PATH];
>    shared_name (buf, PIPE_SW_MUTEX, parent_pty);
>    HANDLE mtx = OpenMutex (MAXIMUM_ALLOWED, FALSE, buf);
> -  WaitForSingleObject (mtx, INFINITE);
> -  ReleaseMutex (mtx);
>    DWORD res = WaitForSingleObject (mtx, INFINITE);
>    if (res == WAIT_OBJECT_0 || res == WAIT_ABANDONED)
>      {
> @@ -2006,9 +2004,8 @@ fhandler_console::pcon_hand_over_proc (void)
>      }
>    else
>      system_printf("Acquiring pcon_ho_mutex failed.");
> +  ReleaseMutex (mtx);
>    CloseHandle (parent_pty_input_mutex);
> -  /* Do not release the mutex.
> -     Hold onto the mutex until this process completes. */
>  }
>  
>  bool
> -- 
> 2.51.0

Other than that, LGTM.


Thanks,
Corinna